Question #ebe44

1 Answer
Jan 14, 2018

Answer:

Here's why.

Explanation:

The idea here is that the calcium cation, #"Ca"^(2+)#, carries a #2+# charge and the hypochlorite anion, #"ClO"^(-)#, carries a #1-# charge, so in order for the two ions to form an ionic compound, they must combine in a #1:2# ratio.

Since ionic compounds are neutral, the overall negative charge coming from the anions must balance out the overall positiev charge coming from the cations.

In this case, you will need #2# hypochloriet anions to get a total negative charge of

#2 xx (-1) = 2-#

in order to balance out the #2+# charge of the calcium cation.

To show that we need #2# hypochlorite anions for every #1# calcium cation, we use parentheses around the hypochlorite anion and a subscript of #2#.

#"Ca"("ClO")_ 2 => "1 formula unit of Ca"("ClO") = {(1 xx "Ca"^(2+)), (2 xx "ClO"^(-)) :}#

The parentheses are used to show that the subscript is applied to both elements that make up the anion, i.e. to #"Cl"# and #"O"#.

By comparison, something like

#"CaClO"_ 2#

would imply that the subscript is only applied to the oxygen atoms, which would be incorrect given the fact that the hypochlorite anion contains #"Cl"# and #"O"#.